A. Field of the Invention
This invention relates to a novel melt spinning process for producing drawn (i.e. molecularly oriented) polyamide yarn having latent crimp in which the latent crimp is imparted to individual filaments of the yarn without the application of any special crimping apparatus or steps. The term "yarn" is used herein to mean a single filament (mono-filament yarn) or a bundle of filaments (multifilament yarn).
B. Description of the Prior Art
Various mechanical techniques are known for imparting crimp to polyamide yarns. Normally, these techniques require the spun yarn to be fully drawn prior to the crimping step. In general, these techniques involve heating a fully drawn polyamide yarn, deforming the hot yarn, then cooling the yarn while it is in the deformed state, and finally removing the deformations from the cooled yarn. One such technique, gear crimping, involves passing drawn polyamide yarn between two gears, the teeth of which intermesh. The speed at which the yarn can travel between the gears is limited and is considerably slower than the capabilities of present day melt spinning equipment. Consequently, gear crimping is normally accomplished by an operation separate from that of spinning and, therefore, has cost disadvantages from the standpoint of commercial operations. On the other hand, even those crimping techniques which may be accomplished at high speeds and thus coupled with the spinning and drawing operations, such as stufferbox crimping or jet texturing, utilize special equipment and require a separate and expensive texturing step following the spinning and drawing steps.
Another technique which has been utilized for imparting crimp to polyamide yarn is that of spinning a conjugate filament in which two dissimilar polyamides of dissimilar properties (e.g. shrinkage) are united nonconcentrically with respect to the filament axis. This technique, however, requires expensive and elaborate equipment for melting and extruding the two polyamides.
An object of the present invention is to provide a simple and effective process for producing a polyamide yarn having latent crimp which avoids the drawbacks of the abovementioned crimping techniques.
Other objects and advantages of the invention will become apparent from the following detailed description thereof.